Hydrogen sulfide releasing oridonin derivatives induce apoptosis through extrinsic and intrinsic pathways

Hydrogen sulfide (H₂S) has been recognized as the third endogenous signaling gasotransmitter following nitric oxide (NO) and carbon monoxide (CO), and exhibits antiproliferative activity against several cancer cells. In order to stably and controllably release H₂S, H₂S donating compound (ADT-OH) was used in the present study and 18H₂S releasing natural ent-kaurane diterpenoid oridonin derivatives were designed and synthesized. Most derivatives showed more potent antiproliferative activities than oridonin against HepG2 and K562 cell lines, while they were lack of sensitivity to HCT-116 and B16 cells. In particular, 12b showed the most potent antiproliferative activities against HepG2, HCT-116 and K562 cells with IC₅₀ values of 2.57, 5.81 and 0.95 μM, respectively. Through cell cycle analysis, 12b caused cell cycle arrest at S phase in K562 cells and G1 phase in HepG2 cells. In Hoechst 33258 staining assay, cell shrinkage and fragmentation of cell nuclei indicated apoptotic morphological changes. Considering the decline of mitochondrial membrane potential and changes in the levels of apoptosis-related proteins, 12b was shown to induce apoptosis through extrinsic and intrinsic apoptosis pathways.